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antidune The sediment bedform generated by fast, shallow flows of water with a Froude number greater than 0.8. Antidunes form beneath standing waves of water that periodically steepen, migrate, and then break upstream. The antidune bedform is characterized by shallow foresets (see CROSS-STRATIFICATION) which dip upstream at an angle of about 10°. Their preservation potential is low, but they can be identified by low-angle (less than 10°) foresets, dipping up-current. Normally antidunes show a close association with upper-flow-regime plane beds.